The following commands allow for managing your subscriptions in the Group buffer. If you want to subscribe to many groups, it's probably more convenient to go to the Server Buffer, and choose the server there using RET or SPC. Then you'll have the commands listed in Browse Foreign Server at hand.
gnus-group-transpose-groups). This isn't really a subscription command, but you can use it instead of a kill-and-yank sequence sometimes.
gnus-group-kill-level). These groups can't be yanked back after killing, so this command should be used with some caution. The only time where this command comes in really handy is when you have a .newsrc with lots of unsubscribed groups that you want to get rid off. S C-k on level 7 will kill off all unsubscribed groups that do not have message numbers in the .newsrc file.
Also see Group Levels.